1. Field of the Invention
This invention relates to a method for applying a substrate, such as a wafer to an assembly carrier, and to a device for accomplishing this method.
2. Description of Related Art
In the commercial production of semiconductor wafers, such as slices of silicon, GaAs and the like, a semiconductor wafer is subjected to different successive processes. An important step after applying various structures and layers on a front side, such as an active side or respectively the side on which the applied structures are located, is the attachment of a protective layer on the active side. This layer protects the upper side of the wafer and thus its sensitive surface during the subsequent treatment process, for example thinning the wafer by grinding or lapping. The thinning process takes place on the rear side of the wafer and significantly influences the residual thickness of the wafer.
Because abrading occurs down to a thickness of approximately 50 μm or less, achieving as flat as possible a surface of the wafer is very important. One parameter for this surface quality is the quality of the wafer substrate which is formed from the assembly carrier and the applied protective layer. Unevenness impairs the rear side of the wafer which is to be processed. Methods for improving the unevenness are known.
PCT International Publication WO 99/25019 describes a special mixture for mounting and disassembling a semiconductor wafer. German Patent Reference DE 43 32 488 discloses a foil attached as flat as possible by adhesive force. Also known are reversible adhesive layers. It has become apparent, that despite expensive preparation of the wafer substrate, there is an inherent disadvantage in the system. Through the introduction of a protective layer between the active side of the wafer and the assembly carrier, air pockets occur which cause unevenness on the rear side of the wafer. These air pockets can scarcely be eliminated by increasing the compressive force or distributing the local pressure locations. Repeating the pressing process several times also does not achieve the desired result. Moreover, the danger of breaking the wafer is increased in an uncontrolled manner by such manipulations.